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            <h2 class="title" style="clear: both"><a id="dbset_h_hash"></a>DB-&gt;set_h_hash()</h2>
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      <pre class="programlisting">#include &lt;db.h&gt;

int
DB-&gt;set_h_hash(DB *db,
    u_int32_t (*h_hash_fcn)(DB *dbp, const void *bytes, 
    u_int32_t length));  </pre>
      <p>
         Set a user-defined hash function; if no hash function is specified, a
         default hash function is used.  Because no hash function performs
         equally well on all possible data, the user may find that the built-in
         hash function performs poorly with a particular data set.
    </p>
      <p>
         The <code class="methodname">DB-&gt;set_h_hash()</code> method configures operations performed using the
         specified <a class="link" href="db.html" title="Chapter 2.  The DB Handle">DB</a>  handle, not
         all operations performed on the underlying database.
    </p>
      <p>
         The <code class="methodname">DB-&gt;set_h_hash()</code> method may not be called after the 
         <a class="xref" href="dbopen.html" title="DB-&gt;open()">DB-&gt;open()</a>  method is called. If
         the database already exists when <a class="xref" href="dbopen.html" title="DB-&gt;open()">DB-&gt;open()</a>  
         is called, the information specified to <code class="methodname">DB-&gt;set_h_hash()</code> must be the same as that
         historically used to create the database or corruption can occur.
    </p>
      <p>
         The <code class="methodname">DB-&gt;set_h_hash()</code> <span>
            <span>
                  method returns a non-zero error value on failure and 0 on success.
            </span>
            
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              <h3 class="title"><a id="idp50386968"></a>Parameters</h3>
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                <h4 class="title"><a id="idp50387160"></a>h_hash_fcn</h4>
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          <p>
                          The <span class="bold"><strong>h_hash_fcn</strong></span> parameter is the
                          application-specified hash function.
                     </p>
          <p>
                          Application-specified hash functions take a pointer to a byte string
                          and a length as parameters, and return a value of type <span class="bold"><strong>u_int32_t</strong></span>. The hash function must handle any
                          key values used by the application (possibly including zero-length
                          keys).
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              <h3 class="title"><a id="idp50382568"></a>Errors</h3>
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        <p>
                         The <code class="methodname">DB-&gt;set_h_hash()</code> <span>
            <span>
                 method may fail and return one of the following non-zero errors:
            </span>
            
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                <h4 class="title"><a id="idp50392336"></a>EINVAL</h4>
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                If the method was called after <a class="xref" href="dbopen.html" title="DB-&gt;open()">DB-&gt;open()</a> 
                was called; or if an invalid flag value or parameter was specified.
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              <h3 class="title"><a id="idp50391256"></a>Class</h3>
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                <a class="link" href="db.html" title="Chapter 2.  The DB Handle">DB</a>  
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              <h3 class="title"><a id="idp50394408"></a>See Also</h3>
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                     <a class="xref" href="db.html#dblist" title="Database and Related Methods">Database and Related Methods</a> 
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